I think it would have a tremendous effect on spam. Imagine if every shit thread by a newbie just never makes it to being published. Every single bot that comes here to spam advertise or spread malware will never be seen publicly and staff can nuke them before they need to be reported and do any damage (which we would have to do anyway). I think the place would be cleaned up immediately, especially from spam by new users.
I like this idea, but not without many more staff. Given that only a fraction of the spam is currently being reported, and it sometimes takes 24-48 hours for these reports to be acted upon in boards without a dedicated mod, it is easy to see how within a few days or weeks a backlog could build up which would never be cleared. Genuine newbies could potentially have their posts lost in this backlog and eventually give up when nothing they write is actually posted. We need more staff to guarantee this doesn't happen.
I would also add a perk to this - earning a set amount of merit allows your posts to bypass the filter. It has to be
earned merit, so all the hero and legendary shitposters get filtered too, but once you have proven you are a substantial poster by earning say 50 merit (example), your posts no longer need approved before posting. This isn't to say that your posts can't still be reported, or even have the privilege removed if you abuse it.
I don't see many people complaining in Meta about their trashed or locked spam mega thread, do you?
I can say from anecdotal evidence (not scientific, I know) that the majority of time the OP in spam mega threads is long gone. I bet most of them don't even realize their post turned in to a spam mega thread, let alone that it has been locked or trashed. For the most part they aren't interested in reading replies - they are only interested in churning out as many low effort posts in the shortest space of time possible.